Track belt guide wheels assembly

ABSTRACT

A track assembly comprising guide wheels in a region of greatest impacts on the guide rails of the track, which are also the regions of greater wearout of the guide rails, the guide wheels being further arranged in a staggered position, thereby yielding a reduction in noise generation.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority on Canadian application no 2,457,999filed on Feb. 17, 2004.

FIELD OF THE INVENTION

The present invention relates to endless track belts. More specifically,the present invention is concerned with a track belt guide wheelsassembly.

BACKGROUND OF THE INVENTION

An endless track belt assembly for propelling a snowmobile over snow,ice, or other similar ground structure typically comprises an endlesselongated body made of polymeric material going around a sprocket wheeland a front wheel, and having a ground-engaging outer surface and aninner surface. The body of the belt may be reinforced with rods. Theinner surface receives and supports, on a lower run thereof, asuspension comprising a plurality of guide wheels, and guide rails. Theground-engaging surface typically bears a series of spaced traction lugmembers or profiles, for transversal rigidity. Clips may further beprovided on the profiles to enhance traction.

As may be seen in FIG. 1(A), small guiding wheels 10 are standardlypositioned transversally in aligned pairs along guide rails 12 of thetrack, shocks being provided between the guide rails 12.

It is known that the noise generated by tracked vehicle such assnowmobiles is essentially produced by the endless belt track thereof.An analysis of a frequency spectrum of the noise generated by a trackedvehicle shows a main peak at a frequency corresponding to a drivingfrequency of the track belt and to harmonics thereof.

The driving frequency F_(e) of the track belt may be calculated from anumber n of tooth of the sprocket wheel and a speed of rotation rpm ofthe sprocket in turn per minute, using the following relation:$F_{e} = \frac{n \cdot {rpm}}{60}$

Since the track has a constant pitch, factors that may modify thedriving frequency thereof may comprise the mounting of the track on thesprocket, an action of the guiding wheels on the reinforcing rods, anaction of the small guiding wheels on the guide rails, an action of thetraction clips on the guide rails and an impact of the profiles with theground, for example.

One of several methods actually contemplated for reducing an occurrenceof peaks in acoustic spectra of tracked vehicle associated withrepetitive events consists of breaking such repetitive sequences bycausing a random spreading of the different events submitted to thetrack. The result is a distribution of energy on different harmonics ofthe critical frequency Fe.

It has been suggested to create such a random spreading by providingnon-regular profiles on the ground-engaging surface of the track forexample.

It has also been suggested to provide clips on each profile of thetrack.

There is still a need in the art for endless track belts producingreduced noise.

SUMMARY OF THE INVENTION

More specifically, there is provided an endless track belt assemblycomprising an endless elongated body going around a sprocket wheel and afront wheel and having a ground-engaging outer surface and an innersurface, the inner surface receiving, on a lower run thereof, asuspension comprising a plurality of guide wheels and guide rails,wherein the plurality of guide wheels comprises guide wheels positionedtransversally in ones of aligned pairs and staggered pairs in a forwardregion of the assembly, one of the pairs being located close to a curvedregion of the forward region of the assembly.

Other objects, advantages and features of the present invention willbecome more apparent upon reading of the following non-restrictivedescription of embodiments thereof, given by way of example only withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the appended drawings:

FIG. 1(A), labelled “Prior Art”, is a schematic diagram of an assemblyaccording to the prior art;

FIG. 1(B) is a is a schematic diagram of an assembly according to anembodiment of the present invention;

FIG. 1(C) is a is a schematic diagram of an assembly according to afurther embodiment of the present invention

FIG. 2 shows a noise frequency spectrum of an assembly as known in theart (dotted lines) and a noise frequency spectrum a vehicle of anassembly according to an embodiment of the present invention (fulllines); and

FIG. 3 shows a noise frequency spectrum of an assembly as known in theart (dotted lines) and noise frequency spectrum of an assembly accordingto a further embodiment of the present invention (full lines).

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

There is provided an assembly for a tracked vehicle, producing reducednoise.

Tests performed on a variety of such conventional assemblies asillustrated in FIG. 1(A) show that the noise generated at the level ofthe guide wheels 10 is highly dependent on a positioning thereof. It isfound that guide wheels located in a rear region or in a centre regionof the assembly are a main source of noise. A zone situated in a forwardregion of the assembly is found to be a silent region.

An assembly according to the present invention is provided with guidewheels located in the forward region of the assembly.

As illustrated in FIG. 1(B), guide wheels 14 may be located in alignedpairs in the forward region of the assembly in such a way that a firstgroup of guide wheels 14 is located close to a curved region 20 of theforward region of the assembly.

As illustrated in FIG. 1(C), the guide wheels 16 may be located innon-aligned pairs in the forward region of the assembly such a way thata first group of guide wheels 16 is located close to a curved region 20of the forward region of the assembly. Therefore, each guide wheel of agiven pair is now in a staggered position with respect to itscounterpart, which contributes to cancel simultaneous occurrences ofimpacts.

It is found that the noise-reduction effect of such a positing of theguide wheels depends on a distance separating the two guide wheels of apair. Along the guide rails 12, the guide wheels are laterally separatedby a distance less than a distance separating two successive profiles ofthe track so as to avoid producing a simultaneity of impacts, and lessthan the pitch of the track so as to allow a sufficient time of impactbetween the guide wheels and the reinforcing rods.

It is found that the staggered position of the guide wheels is all themore efficient in the noise-reduction as it is applied to the pair closeto a point of attachment of the assembly (see pair 22 in FIG. 1C).

Moreover, the guide wheels may be mounted inside or outside the guiderails 12. It is found that such a position relative to the guide rails,when the guide wheels are located in the forward region of the assembly,does not affect the noise generated. However, when the guide wheels arelocated further away from the forward region in the forward region ofthe assembly, either in the center region or in the rear region thereof,a mounting of the guide wheels in between the guide rails 12 results inan increased noise of production.

As may be seen in FIG. 2, such an assembly as illustrated in FIG. 1(C)allows an overall noise reduction of up to 5 dB (A), and a reduction ofup to 9 dB (A) of the main peak of the frequency spectrum (compare thespectrum measured with the present assembly comprising guide wheels in aforward position in full line, with a spectrum measured with aconventional assembly as used in the art, in dotted line).

The assembly may further be improved by mounting clips in each profileof the ground-engaging surface of the track (not shown). As may be seenin FIG. 3, such an assembly is characterised by an overall noiseattenuation of up to 7 dB (A), as well as by a decreasing effect onharmonics of the drive frequency of the track (compare the spectrummeasured with the present improved assembly comprising clips in eachprofile in dotted line, with a spectrum measured with a conventionalassembly comprising clips in each three profile as used in the art, infull line).

It is further shown that providing the belt with apertures such as punchholes in between the profiles also reduces the sound level.

Interestingly, people in the art will appreciate that with such aforward position of the guide wheels further contributes to reducing andpreventing wearout of the guide rails, which is known to occurespecially in a front region.

Therefore, there is provided a track assembly comprising guide wheels ina region of greatest impacts on the guide rails of the track, which arealso the regions of greater wearout of the guide rails, the guide wheelsbeing further arranged in a staggered position.

The track assembly may further comprise clips mounted in each profile ofthe ground-engaging surface of the track, which results in a largerdistance between the track and the guide wheels, thereby reducing aforce of impact during contacts between rods and wheels.

Although the present invention has been described hereinabove by way ofembodiments thereof, it may be modified, without departing from thenature and teachings of the subject invention as described herein.

1. An endless track belt assembly comprising an endless elongated bodygoing around a sprocket wheel and a front wheel, and having aground-engaging outer surface and an inner surface, the inner surfacereceiving, on a lower run thereof, a suspension comprising a pluralityof guide wheels and guide rails, wherein said plurality of guide wheelscomprises guide wheels positioned transversally in ones of aligned pairsand staggered pairs in a forward region of the assembly, one of saidpairs being located close to a curved region of the forward region ofthe assembly.
 2. The endless track belt assembly as recited in claim 1,wherein the guide wheels are positioned transversally in staggered pairsin the forward region of the assembly, each guide wheel of a given pairbeing in a staggered position with respect to a counterpart thereof. 3.The endless track belt assembly as recited in claim 2, wherein a pair ofguide wheels close to a point of attachment of the assembly is in astaggered position.
 4. The endless track belt assembly as recited inclaim 1, wherein the ground-engaging surface bears a series of spacedprofiles.
 5. The endless track belt assembly as recited in claim 4,wherein clips are provided on the profiles.
 6. The endless track beltassembly as recited in claim 4, wherein the endless belt is providedwith aperture in between the profiles.